Rear end construction for propeller-driven vessels



Dec. 26, 1961 L. NlTZKl ETAL REAR END CONSTRUCTION FOR PROPELLER-DRIVEN' VESSELS Filed Jan. 7, 1958 FIG.

5 Sheets-Sheet 1 a 11:4,- r i zd-du. (3M rmpua C; {xi-a ATTORNEY Dec. 26, 1961 L. NlTZKl ETAL 3,014,449

REAR END CONSTRUCTION FOR PROPELLER-DRIVEN VESSELS Filed Jan, 7, 1958 5 Sheets-Sheet 2 INVENTOR 4 Maia A-z BY 4AM. M

ATTORNEY Dec. 26, 1961 L. NlTZKl ETAL 3,014,449

REAR END CONSTRUCTICN FOR PRQPELLERDRIVEN' VESSELS Filed Jan. 7, 1958 5 Sheets-Sheet 5 lNVENTOR BY Maw 13% m m .F #22 ATTORNEY Dec. 26, 1961 L. NlTZKl ETAL REAR END CONSTRUCTION FOR PROPELLER-DRIVEN' VESSEL-S Filed Jan. 7, 1958 5 Sheets-Sheet 4 INVE NTOR kuadr wake ATTORNEY Dec. 26, 1961 L. NlTZKl ETAL 4 REAR END CONSTRUCTION FOR PROPELLER-DRIVEN VESSELS Filed Jan. 7, 1958 5 Sheets-Sheet 5 FIG. 5

United States The present invention relates to a rear end construction for propeller-driven vessels, and more particularly to a bulging portion at the rear end of the hull of a propeller-driven vessel.

Propellers provided on the rear end of standard single propeller vessels, operate in a non-uniform field of velocity. The water through. which the propeller vanes pass has different flow velocities in radial as well as in peripheral direction with respect to the propeller, so that the central axial flow can hardly be utilizedfor the prpulsion of the vessel. Furthermore, the propeller vanes are exposed to differentlydirected flows during rotation of the propeller so that the angle of attack periodically changes whereby periodically varying forces act on each propeller profile located in a different cylinder section. The varying forces produce varying moments which have an eifect on the hull of the vessel, and on the power plant of the same, and produce oscillations, which particularly if the driving power is great and'the machine is provided atrthe. rear end of the vessel, frequently lead to damage on the rudder, propeller, hull, engine, and particularly on the reduction gears driving the propeller shaft.

It isone object of the present invention to overcome the. disadvantages of the rear end constructions of the known propeller-driven vessels, and to provide on the rear endof the vessel, means by which the field of velocity in the plane of the propeller is as far as possible concentric to the axis of the propeller shaft.

Another object of the present invention is to provide an elongated bulging portion on the rear end portion of a hullby which the water is guided in a uniform flow pattern toward the; propeller.

A further object of. the present invention is a rear end construction for the hull of a propeller-driven vessel which preventsvibrations and oscillations of the vessel and its parts during rotation of the propeller.

Withthese objects in view, the present invention mainly consists in a rearend portion of a hull which comprises an elongated bulging portion having a main axis extending in longitudinal direction of the hull and being bounded by an outer surface which isso shaped that sections therethrough taken on parallel planes vperpendicular to the main axis have'the outlines of conic sections. Thereby, the water is guided toward the propeller in a concentric and substantially uniform flow pattern. The propeller is arranged behind the bulging portion, and a frustoart ice Due to the construction of'the bulging portion according to the present: invention together with a corresponding reduction of the deadwood, a held of flow velocity isproduced which is almost-uniformwith respectto the axis of the propeller, except, of course, for the small sector above the propeller where standard spars are provided on the stern of the vessel;

In such field of uniform flow velocity, the propeller has optimal operational conditions, and periodic variations of the forces and moments acting on the propeller are very small; Particularly, the construction of the present invention substantially reduces the eccentricity of the shearing forces which frequently cause breakage of the end portion of the propeller shaft. In accordance with a further modification of the present invention, the irregularities of flow produced by the spars of the main portion of the rear end of the hull above the propeller shaft, can be considerably improved by a guide member arranged above the propeller shaft and the bulging portion.

The novel features which are considered as characteristic for the invention are set forth in particular in the appended claims. The invention itself, however, both as to its construction and its method of operation, together with additional objects and advantages thereof, will be best understood from the following description of specific embodiments when read in connection with the accompanying drawings, in which:

FIG. 1 is a side view illustrating an embodimentrof the present invention; 7

FIG. 2 is a fragmentary rear view of a hull constructed in accordance with the presentinvention;

conical guide portion connects the surface of the bulging portion'with the. surface of the propeller hub.

The" axis of the propeller shaft is preferably slightly inclinedtothe-main axis of. the bulging portion, which is preferably horizontal, and the two axes preferably intersect in the region of" the=frusto,-conical guide portion rearwardly ofthe bulging portion. 7

In the preferred embodiment of the present invention, the conic sections are elliptic below the axis of the propeller shaft, and partly circular above this axis where the bulging portion is connected to the rnainportion of the rear end of the hull. V

The; lowerpart of the outer surface. of the bulging portion; defines the shape of the. so-called. dead wood which are; solid timbers built into the. stern of the vessel where breadth does not permit framing.

FIG. 3 is a schematic view illustrating theflow conditions in the plane of the propeller by lines of. equal flow velocity, and illustrating the conditions prevailing in prior art constructions;

FIG. 4 is a schematic view corresponding to FIG. 3

7 but illustrating the flow conditions. as prevailing in the propeller plane of a vessel constructed in accordance with the present invention; and

FIG. 5 is a vertical sectional view through the stern of the hull forward of the propeller and rudder of the vessel.

Referring now to the drawings, and more particularly to FIG. 1, the rear end portion of a hull has a mainportion 11 which is narrowed behind the suspended rudder 8, and such main portion is bounded at the lower end thereof by an elongated bulging portion 3 having a main axis 6. The surface of the bulging portion 3 merges into. the frusto-conical surface of the. guide portion 2 which projects from the rear end of the hull and surrounds the propeller shaft, not shown, which has an axis 7. A propeller 1 is mounted on the propeller shaft. As can be best seen from FIG. 2 and from FIG. 5, sections taken on parallel planes perpendicular to the main axis. 6-of the bulging portion 3, have. the outlines of conic sections; and more particularly the sections 4 below the propeller shaft have elliptic shape,v while, the sections 5 above the propeller shaftare of part-circular shape which facilitates the constructionofthe hull. The outer surface of the bulgingrportion mergesinto theouter surface of the main portion along two concave surfaces extending upwardly and rearwardly on the sides ofthe hull as indicated by the line it]. It is apparent that the elliptic lower surface 4- determines the leiigth and the shape of the dead wood portion ofthe. hull. Consequently, byselecting suitable conic sections for themaximal improvement of the central flow conditions around thepropeller axis, the optimal dead wood construction can be obtained.

The axis 7 of the propeller 1 is slightly downwardly and rearwardly inclinedand is located in the same vertical plane as the main axis 6 of the bulging portion 3:

3 This vertical plane is at the same time a plane of symmetry for the bulging portion 3.

Above the bulging portion 3, and symmetrically with respect to the above-mentioned vertical plane of symmetry, is arranged an arcuate guide member 9 on the main portion of the rear end of the hull, and this guide member 9 is either twisted, or of conical shape. The guide member 9 is downwardly concave and influences the flow conditions in the region behind the main portion of the rear end of the hull so as toaid in producing uniform flow conditions around the axis of the propeller. It will be noted that the axes 6 and 7 intersect in the region of the frusto-conical guide portion 2 which is arranged directly forwardly of the propeller 1 and projects from the rear end of the hull.

FIGS. 3 and 4 illustrate the flow conditions by isotachs, e.g. lines of equal flow velocity. The isotachs illustrate the flow velocity conditions in a central concentric field surrounding the propeller axis, and have been obtained by tests carried out with models of standard hull constructions as shown in FIG. 3, and with a model of a hull rear end provided with the bulging portion of the present invention as shown in FIG. 4. A comparison of FIGS. 3 and 4 will prove that the lines of equal flow velocity are substantially concentric in the arrangement of the present invention, while they extend in almost tangential direction in the constructions of the prior art. Therefore, a corresponding propeller portion will pass through streams of water having more equal velocity in the construction of the present invention, and will pass through zones of more different fiow velocity in the construction of the prior art. A change of the flow velocity and direction will result in the variation of the angle of attack and of the force acting on the propeller vane, and cause vibrations of the hull.

It will be understood that each of the elements described above, or two or more together, may also find a useful application in other types of hull constructions differing from the types described above.

While the invention has been illustrated and described as embodied in a bulging portion on the rear end of a hull for producing substantially uniform flow conditions around the axis of the propeller, it is not intended to be limited to the details shown, since various modifications and structural changes may be made without departing in any way from the spirit of the present invention.

Without further analysis, the foregoing will so fully reveal the gist of the present invention that others can by applying current knowledge readily adapt it for various applications without omitting features that, from the standpoint of prior art, fairly constitute essential characteristics of the generic or specific aspects of this invention and, therefore, such adaptations should and are intended to be comprehended within the meaning and range of equivalence of the following claims.

What is claimed as new and desired to be secured by Letters Patent is:

1. Rear end portion of a hull comprising a substantially frusto-conical rearwardly tapering guide portion adapted to surround a propeller shaft carrying a propeller rearwardly of said guide portion; and an elongated bulging portion located forwardly of said guide portion and having an outer surface rearwardly tapering and upwardly and rearwardly inclined, said outer surface merging into the surface of said guide portion for guiding water toward the propeller, said outer surface of said bulging portion merging into the outer surface of said main portion along two concave surfaces extending upwardly and rearwardly on the sides of said hull, said bulging portion having a main axis located in the same vertical plane as the axis of the propeller shaft and intersecting with said axis in the region of said guide portion, sections through the lower part of said surface of said bulging portion taken on parallel planes perpendicular to said main axis having the outlines of non-circular conic sections elongated in vertical direction for producing substantially uniform flow conditions around the axis of said propeller.

2. Rear end portion of a hull, comprising a main portion; an elongated bulging portion upwardly and rearwardly inclined and extending along the lower rear end of said main portion, said elongated bulging portion having a main axis extending in longitudinal direction of said hull and an outer surface for guiding water toward a propeller located rearwardly of said bulging portion, sections through the lower part of said outer surface of said bulging portion taken on parallel planes perpendicular to said main axis having the outlines of non-circular conic sections elongated in vertical direction for producing substantially uniform flow conditions around the axis of said propeller; and an arcuate guide member downwardly concave toward said main axis and inclined downwardly and rearwardly, said guide member being secured to said main portion above said bulging portion and being symmetrical to a vertical plane passing through said main axis for further guiding water toward the propeller.

3. Rear end portion of a hull, comprising a main portion; an elongated bulging portion upwardly and rearwardly inclined and extending along the lower rear end of said main portion, said elongated bulging portion having a main axis extending in longitudinal direction of said hull and an outer surface for guiding water toward a propeller located rearwardly of said bulging portion, sections through the lower part of-said outer surface of said bulging portion taken on parallel planes perpendicular to said main axis having the outlines of non-circular conic sections elongated in vertical direction for producing substantially uniform flow conditions around the axis of said propeller; and a twisted guide member inclined downwardly and rearwardly, said guide member being secured to said main portion above said bulging portion and being symmertical to a vertical plane passing through said main axis for further guiding water toward the propeller.

4. Rear end portion of a hull comprising a main portion; a substantially frusto-conical rearwardly tapering guide portion adapted to surround a propeller shaft carrying a propeller rearwardly of said guide portion; and an elongated bulging portion located forwardly of said guide portion and having an outer surface upwardly and rearwardly inclined, and rearwardly tapering and merging into the surface of said guide portion for guiding water toward the propeller, said outer surface of said bulging portion merging into the outer surface of said main portion along two concave surfaces extending upwardly and rearwardly on the sides of said hull, said bulging portion extending along the lower rear end of said main portion, and said guide portion being located rearwardly of said main portion, said bulging portion having a main axis located in the same vertical plane as the axis of the propeller shaft and intersecting with said axis of the propeller shaft in the region of said guide portion, sections through said surface of said bulging portion taken on parallel planes perpendicular to said main axis having the outlines of conic sections and having elliptic shape at least below the level of said main axis elongated in vertical di rection for producing substantially uniform flow conditions around the axis of said propeller; and an arcuate guide member inclinde downwardly and rearwardly, said guide member being concave in downward direction and secured to said main portion above said bulging-portion and being symmetrical to a vertical plane passing through said main axis for further guiding water toward the pro peller.

References Cited in the file of this patent UNITED STATES PATENTS Sturtevant Nov. 25, 1890 751,158 Flindt Feb. 2, 1904 5 v V 6 UNITED STATES PATENTS 1 266,409 Great Britain Mar. 3, 1927 8 4 4 P 1 N I 4 1905 388,103 Great Bntam NOV. 27, 1930 21 21 1 11%, 1930 493 596 Canada 1 1 6. 1953 1,780,998 Curioni Nov. 11, 1930 5 OTHER REFERENCES 2,283,291 Selden May 19, 1942 8 2,747,536 Russell y 29, 1956 A.P.C. apphcatlon of Klmdwort, Senal Number 3 3,

215, published May 11, 1943.

FOREIGN PATENTS 137,513 Austria May 11, 1934 

